You know it when you hear it.

It. The music that breaks your heart. The music that transports you. The music that reminds you of who you deeply are.

Music. That amazing, elusive, beautiful creation – the essential expression of what it is to be alive. Every culture needs music, and it is our one universal language. It carries meaning which words have yet to compose. Music – the talisman of the spirit; the midwife of the soul.

Being a singer of sorts, I have long studied what happens to people when they witness music in performance.

Little does an audience know how carefully the singer scrutinises his crowd. As his eye surveys the scene in front of him, it is true that he may be lost in the meaning of the moment. However, he may also be evaluating the chipped paintwork above the klieg light trained upon him. But more likely, he may be engaged in observing how the sound he makes affects the most precious of possessions: his audience.

It is remarkable how much in music is circular. From the resonance of any one note, to the reciprocal energy that completes any performance. As if to belabour the point, the song whose effects I wish to describe begins with an O. One big, announcing circle.

O, Holy Night is, in fact, the translation of a French hymn written in the 1800s, with an original text which feels somewhat unremarkable; the language and servile tone was commonplace for religious texts of the time, I suspect.

But the hymn achieves lift-off in its English version. If ever a translation were transubstantiated, it is this. O, Holy Night tells a story of divine simplicity, full of tenderness and pathos.

‘A thrill of hope, the weary world rejoices’

Once this line is sung, some implicit wisdom tells us that we are in the hands of a master.

But it is the music that gives O Holy Night its timelessness. The beautiful, lifting symmetry of its open chords. The shape of its melody, like the ascent of some promontory of Sinai, carrying to the summit, only to be greeted with a most glorious descent.

I have studied many audiences as they listen to this carol being performed. When witnessed, its perfected music appears more effervescent than it is. But its roots, I have come to realise, are profound.

O, Holy Night is the voice of the known and the unknown, in synchrony. Not only does it relate the magic of a transcendent story, it finds a place for our terrestrial voices too.

We are the choir. And it is only when the choir appears that the audience connects fully with the message of O, Holy Night.

‘Fall on your knees! Hear the angel voices!’

These words, dramatic and absolute, are echoed in several harmonic lines with restrained sensitivity. O, Holy Night then ceases to be a performance. It becomes collaboration.

‘O night…..divine!’

I have seen men and women weep as this moment flows through them. I have seen children pull closer to their mothers’ arms as the swell of the choir echoes that one celestial voice. I have known singers to temporarily lose control of their notes, such is the perfection of text, harmony and melody in one climactic phrase.

So what is this thing?

This thing that music gives to us, with such unknowing generosity, and with such little expectation of anything in return? What is it that we hear?

It is, I suspect, the voice of nature. The voice of our own humanity. And yes, I will say it: the voice of god.